1. Field of the Invention
This invention relates to a projection type display apparatus, and particularly to a projection type display apparatus attaining a great improvement in light utilizing efficiency or the thinning of the apparatus in an oblique projection system.
2. Related Background Art
An apparatus of this kind is disclosed, for example, in Japanese Patent No. 2893877. The construction of a basic optical system according to this example of the prior art is shown in FIG. 6 of the accompanying drawings. In this example of the prior art, a trapezoidal intermediate image is formed on a reflecting mirror 49, and it is obliquely projected onto a screen 53 by a projection lens 40. As regards the trapezoid rate of this intermediate image, the trapezoid rate of an inverted trapezoid is set so as to just cancel trapezoid distortion created by the oblique projection onto the screen 53.
In the above-described example of the prior art, however, the trapezoid distortion is cancelled and corrected, but the principal ray of reflected light reflected by the reflecting mirror 49 on which the intermediate image is formed does not coincide with the optical axis of the projection lens 40 at all and therefore, as shown in FIG. 6, only the other divergent light beam than the principal ray passes to the projection lens 40. Therefore, the quantity of light which can be utilized is slight, and this example of the prior art has a problem in that light utilizing efficiency becomes very bad.
It is an object of the present invention to solve the above-noted problem peculiar to the prior art and to provide, in a projection optical system for correcting trapezoid distortion occurring to an intermediate image by oblique projection, a super-thin projection type display apparatus which can achieve a great improvement in light utilizing efficiency and can accomplish the projection of a large image plane.
It is also an object of the present invention to provide a projection type display apparatus which comprises:
a first projection optical system for obliquely projecting light from an original picture onto a predetermined surface, the first projection optical system forming the intermediate image of the original picture on or near the predetermined surface;
a second projection optical system for obliquely projecting the light from the predetermined surface onto a surface for projection and imaging it thereon; and
light deflecting means disposed between the first projection optical system and the second projection optical system for deflecting the light emerging from the first projection optical system;
wherein the optical axis of the first projection optical system is deflected by the light deflecting means so as to substantially coincide with the optical axis of the second projection optical system.
In the foregoing, xe2x80x9cnearxe2x80x9d appearing in xe2x80x9cthe first projection optical system forming the intermediate image of the original picture on or near the predetermined surfacexe2x80x9d means a range within which the intermediate image can be regarded as being formed substantially on the predetermined surface, including a case where the positions of xe2x80x9cthe predetermined surfacexe2x80x9d and xe2x80x9cthe intermediate imagexe2x80x9d slide a little in parallelism to each other, and a case where the two intersect with each other. That is, it means that when an observer disposes a screen or the like on the predetermined surface and observes the intermediate image of the original picture, the positions of the predetermined surface and the intermediate image are near to each other to such a degree that the intermediate image can be observed within a range in which a feeling of resolution is sufficiently obtained to the observer.
In one aspect of the invention, the light deflecting means is disposed on the predetermined surface.
In further aspect of the invention, the light deflecting means is constituted by a transmission type diffracting optical element.
In further aspect of the invention, the light deflecting means is constituted by a reflection type diffracting optical element.
In further aspect of the invention, the light deflecting means is a hologram.
In further aspect of the invention, the light deflecting means is disposed at or near the position of the intermediate image.
In further aspect of the invention, the surface for projection has an eccentric Fresnel lens.
In further aspect of the invention, the surface for projection has a plurality of eccentric Fresnel lenses.
In further aspect of the invention, the surface for projection has a lenticular lens.
In further aspect of the invention, the light deflecting means has the light deflecting action and the light condensing action.
In further aspect of the invention, the projection type display apparatus has a plurality of vertically or substantially vertically disposed reflecting mirrors.
In further aspect of the invention, the projection type display apparatus is of a rear projection type projecting an image from the rear onto the surface for projection.